This invention relates to static pressure probes, and relates more particularly to such type probes which are disposed approximately perpendicularly or more to an airstream, and preferably disposed in the downstream direction of the airstream and which are subject to plugging by particle contamination and/or icing.
Such static pressure probes are utilized in aircraft for measuring ambient static pressure, or in other applications such as in measuring the static pressure of airflow in turbomachinery. In any case various applications of static pressure probes contemplate the utilization of an aperture or orifice for receiving a sample of the airflow whose pressure is being measured, characteristically such orifice facing downstream relative to the airflow. In this manner the static pressure probes are distinguished from venturi or total pressure probes which characteristically have an opening facing upstream into the airflow.
Such pressure probes are utilized for either output reading of the parameter being measured, and/or in control systems for performing various functions, such as in the fuel control system of turbomachinery. It is well known that plugging, either by particle contamination and/or icing, will render such static pressure probe inoperative and deleteriously affect operation of the machinery with which it is associated. In aircraft applications, icing at high altitudes has many times become a critical problem of operation.
Various schemes for avoiding these problems have been considered previously. Generally such schemes center about concepts for passing a heating airflow in the general area of the pickup orifice to prevent icing, and/or utilization of a removable hood which is mounted over the orifice when not in use, and then removed when the pressure probe is in use. Obviously, ducting of heating airflow to a small pressure probe orifice presents several problems of operability, economy, reliability, as well as introducing substantial complexity into an otherwise relatively simple device. It will also be apparent that utilization of a removable hood when the tube is not in use is of no consequence in avoiding particle contamination and/or icing during use of the pressure probe. Exemplary discussions of prior art structures may be found in U.S. Pat. No. 3,535,930 which relates to heating of the probe; U.S. Pat. Nos. 2,488,810; 2,532,316; 2,786,353 all of which relate to removable covers for upstream facing pitot tubes; U.S. Pat. No. 101,858 which relates to an upstream facing pitot-static tube; and U.S. Pat. No. 3,347,095 which is indicative of prior art static pressure probes subject to icing and/or particle contamination.